Abstract: The fluid-solid coupling method was used in the finite element analysis of the effect of deep excavation dewatering on the deformation of the excavation supporting structures and the adjacent soils of a cut and cover tunnel in the lake in Xiamen City. The three-dimensional model was established by using commercial finite element method software PLAXIS and considering the site specific soil conditions. The entire installation of the supporting structure for the deep excavation, dewatering and excavation process are numerically simulated. The stress and deformation in each stage of the construction are evaluated. The results indicate that, under the fluid-solid coupling approach, no convergence could be obtained in the original design. As a result of the numerical analysis, the passive zone underneath the excavated area were improved by the deep mixing method. After the soil improvement in the passive soil zone, the deformation in the supporting structure and the settlement in the surrounding soils reduced. Along the longitudinal direction of the excavated area, the variation of the stress on the strut could be more than 100%. In the excavated area, the bottom deformation in the wider area had much larger deformation than other locations and the lateral movement and bending moment in the supporting structure were also improved. The results also showed that the fluid-solid coupling approach can improved the reliability of deep excavation supporting in complicated soil and spatial conditions.

Key words: Tunnel Underneath the Lake, Numerical Simulation, Deep Excavation Construction, Fluid-Solid Coupling Approach, Construction Effect